Dies used in the manufacture of extruded metal parts such as ones formed from aluminum, magnesium or similar metals are subjected to extremely high forces and, therefore, must be designed with sufficient strength to withstand such forces without excessive distortion or cracking. Additionally, such dies must be capable of consistently forming the extruded part to accurate dimensional tolerances, preferably within the range of 0.003 to 0.010 inches in any cross-sectional dimension.
The prior art discloses a number of extrusion dies and methods for forming. For example, U.S. Pat. No. 4,862,728 discloses an extrusion die which is negatively tapered essentially throughout its length at an angle of at least 1.degree. such that any friction stress between the die lands and metal flowing through them is negligible. This patent describes certain advantages which it purports to have over conventional extrusion dies such as that shown and described in FIG. 1 thereof. The foregoing patent, including the problems with respect to the prior art extrusion dies, is incorporated herein by reference and a copy of such patent is enclosed herewith.
With respect to the extrusion die and method of forming disclosed in U.S. Pat. No. 4,862,728, its design provides that a sharp corner function as its bearing surface which determines the cross-sectional configuration of the extruded part and that a short tapered section or die land 20 generally ". . . not more than about 2 mm" extend downstream from said corner bearing surface. (See column 2, lines 54 and 55). The die downstream of such tapered die land 20 has an aperture defined by a cambered depression 22 which can result in a potential flexing or distortion when material is extruded therethrough due to insufficient support of the cantilevered section forming the die land 20. (See specifically the lack of support outwardly of the corner 24). Additionally, since the length of the die aperture intended to determine the cross-sectional configuration of the extruded article is zero, there is a question of whether it is sufficient to equalize the flow of the metal.